Conventionally, miniature unmanned aerial vehicles (UAVs) which are typified by unmanned helicopters for industrial use have been expensive and hard to obtain and manipulative skills have been needed to make them fly stably. Recently, however, airframe price has fallen because an acceleration sensor, angular velocity sensor, microcontroller, etc. which have high performance and are easy to handle have become available at reasonable cost, and maneuverability has improved dramatically, since many operations to control and manipulate the airframe have been automated. Because of background circumstances as above, attempts are now made to apply, especially, miniature multicopters to diverse missions in a wide range of fields, not only for hobby purposes.
A multicopter is one type of helicopter equipped with a plurality of rotors, which is a rotorcraft that flies while keeping balance of the airframe by controlling the rotating speed of each of these rotors. Since a multicopter can employ a propeller with simpler structure than that of a helicopter, the multicopter is easy to maintain and its airframe can be built at comparatively low cost.